1. Field of the Invention
The present invention relates to a method of manufacturing magnetic tape and, more particularly, to a method of manufacturing magnetic tape such as tape for computer data backup, audiotape and videotape.
2. Description of the Related Art
In a method of manufacturing various types of magnetic tape such as tape for computer data backup, audiotape and videotape, a wide web-like magnetic tape material wound in roll form is drawn out from the delivery side, and slit into a plurality of narrow magnetic tapes by use of a slitter while being transported, and the magnetic tapes are wound on cores on the winding side.
A conventional slitter used in the manufacturing of magnetic tapes is a device that slits a wide web-like magnetic tape material into a plurality of magnetic tapes by use of pairs of upper and lower rotary blades. The rotary blades are generally constituted by a plurality of rotary blades formed as bed knives in roller form and a plurality of rotary blades in thin disk form, which perform slitting by giving a shearing force to the magnetic tape material between the rotary blades.
In order to obtain a good coil shape in the take-up step in the manufacturing of the magnetic tape material used in manufacturing such magnetic tape, the tape material is wound around in the shape of a crowned roll in which the thickness of the middle portion of the roll is larger than the thickness of both ends of the roll. That is, in a magnetic tape material before slitting into a plurality of magnetic tapes, the outside diameter of the middle portion of the roll is larger than the outside diameter of both ends of the roll.
When this magnetic tape material is slit into a plurality of magnetic tapes, a magnetic tape material taken from the middle portion of the roll and magnetic tape materials taken from both ends of the roll have different lengths, thereby causing the slack of magnetic tapes or the generation of extreme tension in magnetic tapes. This causes the problem of poor running of magnetic tapes due to the slack of magnetic tapes, the problem of variations in the tape width of magnetic tape products due to the tension of magnetic tapes, etc.
Moreover, cleaning devices each provided with a polishing head are often provided in the transporting paths of magnetic tapes. Then, if there are variations in the tension of magnetic tapes, a polishing head coming into contact with a magnetic tape under low tension is apt to be especially worn, thus causing a problem as is often pointed out.
However, the tension control of magnetic tapes by guide rollers used in conventional apparatuses for manufacturing magnetic tape is performed by use of a single guide roller (for example, a grooved suction drum) for a plurality of magnetic tapes. For this reason, these conventional apparatuses are inadequate for solving the above-described problems.
On the other hand, as disclosed in Japanese Patent Application Publication No. 2001-187660, for example, there is a proposal involving reducing the tension cutoff capacity which causes the tension of an upstream magnetic tape to differ from the tension of a downstream magnetic tape. It is said that the occurrence of problems as described above can be reduced by using devices incorporating such a proposal.
However, even when various known devices are adopted, it is difficult to make the tension of individual magnetic tapes completely uniform, and possibility that problems due to the slack of magnetic tapes etc. might arise has not been dismissed as yet.